1. Field of the Invention
The present invention is directed generally to optical systems and more particularly to optical systems having more than one light source.
2. Cross Reference to Related Application
The present application is related to U.S. patent application Ser. No. 495,236, filed concurrently herewith, entitled Redundant Lamp Control Circuit, and assigned to the same assignee as the present invention.
3. Description of the Prior Art
In various types of optical systems it is desirable to have multiple or redundant lamps. The provision of redundant lamps enables the optical system to continue functioning in the event that the primary lamp should fail. Such a feature is particularly desirable in, for example, surgical lights.
In U.S. Pat. No. 4,734,625, a control circuit is disclosed which controls the operation of electric lights. The control circuit may be used in conjunction with a surgical light including a lamp having two filaments. Each filament may be arranged so that it provides an illumination pattern of a different type. In the event one of the filaments fails, the good filament is automatically energized thereby enabling the light to continue operation. Although such a light can continue operating in the event of a filament failure, the pattern for which the failed filament was responsible can no longer be used.
Another example of a controller used for controlling the operation of a multi-filament lamp is found in U.S. Pat. No. 4,458,179.
Another way to address the problem is to provide multiple lamps rather than lamps having multiple filaments. A surgical light utilizing multiple lamps is sold by Martin under the trademark CHROMOPHARE. The CHROMOPHARE lights sold under model nos. C950 and C570 are equipped with auxiliary lamps. Should a lamp burn out, a relay switch energizies one of the auxiliary lamps.
Whether a light is provided with a lamp having multiple filaments or multiple lamps, in either case, the light will not perform in exactly the same manner as with the primary filament or the primary lamp because the backup light source is not at the same focal point. Even the very small change associated with energizing a different filament within the same lamp results in light being produced from a source which is not located at the desired position. Therefore, some compromise in operating characteristics must be made to enable the optical system to continue operating. Thus, the need exists for an optical system which can remain operational with no loss or change in optical characteristics upon the failure of the main light source and energization of a backup light source.